bug#18410: Use SAFE_ALLOCA etc. to avoid unbounded stack allocation.

[Stefan Monnier]

>> Perhaps some of that discussion is moot now, with the stack overflow
>> checking that Dmitry added last month?
> I'd say it's definitely moot on systems where that stack-overflow code
> is working.

I disagree.  Even if the new stack-overflow code works, it doesn't
change the fact that a stack-overflow is a problem for the end-user and
we should try to avoid causing such things.

IOW, Dmitry's overflow-handling is good because it makes the failure
a bit cleaner, but it's still a failure that we should strive to avoid.


        Stefan